Tag Archives: migration

Pick and mix 11 – Another ten links to look at

I’m still on holiday in France so just a series of links this week.


Links to things I thought interesting (picture is the room door of the Ibis Style hotel we stayed at in Paris)

 

Is “novelty” holding science back?

Using radio tagging to improve the conservation of stag beetles

How ‘Nature’ keeps us healthy, from potted plants to hiking

How scientists at Rothamsted Research and the University of North Texas have engineered a relative of cabbage to produce fish oil

Agricultural efficiency will feed the world, not dogma

A really interesting article about migration and movement of people

Dave Goulson’s work on pesticide residues in garden plants summarised by plant ecologist Ken Thompson

Using a field journal to strengthen learning

At the risk of seeming big-headed an interesting episode of Entocast

I don’t normally post about birds but after this golden oriole

committed suicide against our patio doors thought that this deserved a mention

 

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Not all aphids get lost

Although aphids are very good at kicking, we know that aphids would not be very good at football as they are very short-sighted (Doring et al., 2008) but does that mean that they are not very good at finding their host plants? There is a common misperception, and not just confined to non-entomologists, that aphids are no more than aerial plankton. In 1924 Charles Elton

Lost 1

whilst on an expedition to Nordaustlandet* (the second largest of the Spitsbergen group and almost entirely covered by ice) reported finding large numbers of aphids, many still alive, later identified as Dilachnus piceae (now known as Cinara piceae) (Elton, 1925).

Lost 2

Cinara piceae the Greater Black Spruce Aphid –big and beautiful.

 

He suggested that the aphids came from the Kola Peninsula, a distance of about 800 miles (almost 1300 km) due to the strong south and south-east winds blowing at the time. He estimated that they would have made the journey within twelve to twenty-four hours. This was regarded as being an example of totally passive migration and used as one of many examples of aerial plankton** (Gislen, 1948). This is, however, probably not giving aphids credit for what they are capable of doing when it comes to flight. Berry & Taylor (1968), who sampled aphids at 610 m above the grounds using aeroplanes, implied that the aphids, although using jet streams, were flying rather than floating (page 718 and page 720) and that they would descend to the ground in the evening and not fly during the night.

Lost 3

Aphids don’t usually fly during the night. (From Berry & Taylor (1968)).

Dixon (1971) interprets this somewhat differently and suggests that the “movement of the air in which it is flying determines the direction of its flight and the distance it will travel” but then goes on to say “after flying for an hour or two aphids settle indiscriminately on plants”. So yes the speed of the air in which the aphid is flying will determine how far it flies in a set time, but as aphids can fly much longer than an hour or two, active flights of from between 7-12 hours have been recorded (Cockbain, 1961), this rather suggests that the aphids are making a “decision” to stop flying and descend from the jet stream. That said, in the words of the great C.G. Johnson “aphids are weak flyers”, they cannot make progress against headwinds of more than 2 km per hour (Johnson, 1954), although Trevor Lewis gives them slightly more power and suggests that the can navigate against winds of up to 3 km per hour (Lewis, 1964).

Whatever the upper limit is, it doesn’t mean that they are powerless when it comes to ‘deciding’ when to stop flying. In the words of Hugh Loxdale and colleagues, “aphids are not passive objects” (Loxdale et al, 1993). Aphidologists, were until the 1980s (Kennedy, 1986), generally somewhat sceptical about the ability of aphids to direct their flight in relation to specific host finding from the air and not just flying towards plants of the right colour (Kennedy et al., 1961), or at all after take-off (Haine, 1955). The general consensus now, is that aphids control the direction of their flight in the boundary layer*** but that it is determined by the wind at higher altitudes (Loxdale et al., 1993).   Whilst we are discussing viewpoints, another point of debate is on whether aphids migrate or not. Loxdale et al., (1993) state that “migration can be viewed ecologically as population redistribution through movement, regardless of whether deliberate of uncontrolled or from the behavioural viewpoint of a persistent straightened-out movement affected by the animal’s own locomotory exertions or by its active embarkation on a vehicle”. In the case of aphids the vehicle could be the wind. Under both definitions, aphids can be defined as undertaking migrations. Long-distance migration by aphids is defined as being greater than 20 km and short-distance (local) migration being less than this (Loxdale et al., 1993). Long-distance migration is likely to be the exception rather than the rule with most aphids making local flights and not venturing out of the boundary layer, sometimes travelling distances no more than a few hundred metres (Loxdale et al., 1993).

There are different types of winged aphids (morphs) and these show different angles of take-off and rates of climb.  In Aphis fabae for example, which host –alternates between spindle and bean, the gynoparae which migrate from the secondary host to the primary host, have a steeper angle of take-off and climb more rapidly than the alate exules which only disperse between the secondary host plants (David & Hardie, 1988).

Lost 4

http://influentialpoints.com/Images/Rhopalosiphum_padi_emigrant_alate_departing_from_primary_host_c2013-05-21_11-25-12ew.jpg

The gynoparae are thus much more likely to end up in the jet stream and be carried longer distances, with, of course, a greater chance of getting lost (Ward et al., 1998). The alate exules however, may only land in the next field or even in the same one, and easily find a new host plant (Loxdale et al., 1993). These differences between the morphs of host alternating aphids are also seen in the bird cherry-oat aphid Rhopalosiphum padi (Nottingham et al., 1991).  Once safely air-borne, the aphids then have another set of problems to overcome.

How do they ‘decide’ when to land? How do they ‘know’ that there are host plants below them? Aphids have two main senses that help them locate their host plants, vision and smell (odour recognition) (Kring, 1972; Döring, 2014). Generally speaking, aphids respond positively to what we perceive as green or yellow light and negatively to blue and red light (Döring & Chittka, 2007) although this is not an absolute rule. Some aphids are known to preferentially choose yellowing leaves (sign of previous infestation) e.g. Black Pecan Aphid Melanocallis caryaefoliae (Cottrell et al., 2009) which indicates a pretty sophisticated host finding suite of behaviours. Aphids in flight chambers will delay landing if presented with non-host odours even in the presence of a green target (Nottingham & Hardie, 1993) and conversely can be attracted to colourless water traps that have been scented with host plant odours (Chapman et al., 1981). Aphids are thus using both visual and olfactory cues to locate their host plants and to ‘decide’ when to descend from the jet stream or boundary layer (Kring, 1972; Döring, 2014). They are not merely aerial plankton, nor are they entirely at the mercy of the winds, they do not deserve to be described as passive (Reynolds & Reynolds, 2009).

Once at ground level and on a potential host plant, aphids go through a complicated suite of behaviours to determine if the host is suitable or not; if the plant meets all the required

Lost 5

From air to plant – how aphids chose their host plants – after Dixon (1973).

 

criteria, then the aphid will start feeding and reproducing. It is interesting to note that although there may be a lot of aphids in the air, the number of plants on the ground that

Lost 6

Settled safely and producing babies 🙂

http://beyondthehumaneye.blogspot.co.uk/2012/06/aphids.html  https://simonleather.files.wordpress.com/2016/04/cd0a4-aphidbirth2small.jpg

 

are infested with them is relatively low, about 10% in a diverse landscape (Staab et al., 2015), although in a crop, the level of infestation can approach 100% (e.g. Carter et al., 1980). The fact that in some cases less than 1% of those that set off will have found a host plant (Ward et al., 1998) is not a problem when you are a member of clone; as long as not all of the members of a clone gets lost the journey has been a success.

They may be small, they may be weak flyers, but enough of them find a suitable host plant to keep the clone alive and kicking; not all aphids get lost.

 

References

Carter, N., Mclean, I.F.G., Watt, A.D., & Dixon, A.F.G. (1980) Cereal aphids – a case study and review. Applied Biology, 5, 271-348.

Chapman, R.F., Bernays, E.A., & Simpson, S.J. (1981) Attraction and repulsion of the aphid, Cavariella aegopodii, by plant odors. Journal of Chemical Ecology, 7, 881-888.

Cockbain, A.J. (1961) Fuel utilization and duration of tethered flight in Aphis fabae Scop. Journal of Experimental Biology, 38, 163-174.

Cottrell, T.E., Wood, B.W. & Xinzhi, N. (2009) Chlorotic feeding injury by the Black Pecan Aphid (Hemiptera: Aphididae) to pecan foliage promotes aphid settling and nymphal development. Environmental Entomology, 38, 411-416

David, C.T. & Hardie, J. (1988) The visual responses of free-flying summer and autumn forms of the black bean aphid, Aphis fabae, in an automated flight chamber. Physiological Entomology, 13, 277-284.

Dixon, A.F.G. (1971) Migration in aphids. Science Progress, Oxford, 59, 41-53.

Dixon, A.F.G. (1973) Biology of Aphids, Edward Arnold, London.

Döring, T.F. & Chittka, L. (2007) Visual ecology of aphids – a classcial review on the role of colours in host finding. Arthropod-Plant Interactions, 1, 3-16.

Döring, T., Hardie, J., Leather, S.R., Spaethe, J., & Chittka, L. (2008) Can aphids play football? Antenna, 32, 146-147.

Döring, T. (2014) How aphids find their host plants, how they don’t. Annals of Applied Biology, 165, 3-26.

Elton, C.S. (1925) The dispersal of insects to Spitsbergen. Transactions of the Entomological Society of London, 73, 289-299.

Gislen, T. (1948) Aerial plankton and its conditions of life. Biological Reviews, 23, 109-126.

Haine, E. (1955) Aphid take-off in controlled wind speeds. Nature, 175, 474-475

Johnson, C.G. (1951) The study of wind-borne insect populations in relation to terrestrial ecology, flight periodicity and the estimation of aerial populations. Science Progress, 39, 41-62.

Johnson, C.G. (1954) Aphid migration in relation to weather. Biological Reviews, 29, 87-118

Kennedy, J. S., Booth, C. O. & Kershaw, W. J. S. (1961). Host finding by aphids in the field III Visual attraction. Annals of Applied Biology, 49, 1-21.

Kring, J.B. (1972) Flight behavior of aphids. Annual Review of Entomology, 17, 461-492.

Lewis, T. (1964) The effects of shelter on the distribution of insect pests. Scientific Horticulture, 17, 74-84

Loxdale, H. D., Hardie, J., Halbert, S., Foottit, R., Kidd, N. A. C. &Carter, C. I. (1993).The relative importance of short-range and long-range movement of flying aphids. Biological Reviews of the Cambridge Philosophical Society, 68, 291-312.

Nottingham, S.F., Hardie, J. & Tatchell, G.M. (1991) Flight behaviour of the bird cherry aphid, Rhopalosiphum padi. Physiological Entomology, 16, 223-229.

Reynolds, A.M. & Reynolds, D.R. (2009)  Aphid aerial desnsity profiles are consistent with turbulent advection amplifying flight behaviours: abandoning the epithet ‘passive’. Proceedings of the Royal Society B, 276, 137-143.

Staab, M., Blüthgen, N., & Klein, A.M. (2015) Tree diversity alters the structure of a tri-trophic network in a biodiversity experiment Oikos, 124, 827-834.

Ward, S.A., Leather, S.R., Pickup, J., & Harrington, R. (1998) Mortality during dispersal and the cost of host-specificity in parasites: how many aphids find hosts? Journal of Animal Ecology, 67, 763-773.

 

Post script

Political and geographic borders are not factors that deter aphid migrants, Wiktelius (1984) points out that aphids regularly make the journey across the Baltic in both directions to and from Sweden.

Wiktelius, S. (1984) Long range migration of aphids into Sweden. International Journal of Biometeorology, 28, 185-200.

 

*Elton refers to it as North-East Land

** Johnson (1951) objects to this terminology in no uncertain terms. That said, as there are records of non-winged aphids being caught by aircraft (Kring, 1972), it does suggest that there may be some accidental migration going on.

*** The UK Met Office defines the boundary layer as “that part of the atmosphere that directly feels the effect of the earth’s surface” and goes on to say that depending on local conditions it can range in depth from a few metres to several kilometres.

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Not all aphids have wings

Given that aphids are commonly known as green-fly or black-fly, it might be presumed that all aphids are capable of flight. Although this is almost certainly universal at the species level (but see Post script) it is not true within a species. As I have described in an earlier post aphids are possessed of extremely complex and fascinating (to me at least) life cycles. Depending on the species, either most stages of the life cycle are winged (alate) as adults, e.g. the sycamore aphid Drepanoisphum platanoidis

Holocyclic.png

Sycamore aphid

I couldn’t resist showing you this beautiful picture of an adult sycamore aphid borrowed from the best aphid web site that I know of (see http://influentialpoints.com/Gallery/Drepanosiphum_platanoidis_common_sycamore_aphids.htm)

 

Other aphid species, such as my favourite, the bird cherry-oat aphid, Rhopalosiphum padi, only produce alate morphs at specific times of year or in response to changes in host plant quality or crowding.

Heteroecious

 RhopalosiphumPadi  Rhopalosiphum padi on leaf

Winged (alate) and non-winged (apterous) morphs of Rhopalosiphum padi.

In species such as the sycamore aphid, the only apterous morph tends to be the sexual female or ovipara, which has no need to disperse and after mating lives only long enough to develop and lay its eggs on the bark of sycamore trees.

Sycamore ovip on bark

Ovipara of the sycamore aphid searching for an oviposition site

In those species such as the bird cherry-oat aphid, the winged forms are very different from the non-winged forms, not just in terms of their wings but in their physiology, behaviour and life history traits (Dixon, 1998). The role of the winged morphs is to find new host plants and to start new colonies. They have long antenna, long legs and well-developed and many, sensory organs (rhinaria). They are the dispersal stage, or in the case of winged males, the mate seekers. They respond more readily to host odours; they need to be able to find new host plants at a suitable physiological stage and preferably free of natural enemies. A well-developed olfactory system is thus called for.

If you cut them open (preferably anaesthetizing them first), and remove their ovaries, you will find that they have ovarioles with only a few embryos in each chain and that most of the embryos are not mature i.e. without eye spots. In addition, if you cut open a number of individuals from the same clone you will find that they will not all have the same number of ovarioles. For example, the alate exules (winged forms produced on the secondary host plants )of Rhoaplosiphum padi, the number of ovarioles can range from four to ten (Wellings et al, 1980). This variability of ovariole number in the dispersal morphs of aphids that spend much of their life cycle on ephemeral host plants is quite common (Leather et al 1988).  So why do so many aphid species have variable numbers of ovarioles in their alate morphs?

Shaw (1970), showed that there appeared to be three types of black bean aphid (Aphis fabae) alate exules; migrants, those that flew before depositing nymphs, flyers, those that deposited a few nymphs before flying, and non-flyers, those that stayed and reproduced on their host plant. He postulated that this was an adaptation in response to host quality, the worse state the plant was in the more likely the migrant morph would be produced. Many years later Keith Walters and Tony Dixon (Walters & Dixon, 1983) were able to show that there was a very strong relationship between reproductive investment (number of ovarioles) and flight willingness and ability. The more ovarioles an aphid had, the less likely it was to want to take off and fly, and in addition those with more ovarioles could not fly for as long or as far as those with fewer.

Ovarioles and flight

In other words a trade-off between fecundity and migration. As long distance aphid migration is very costly (very few survive, Ward et al, 1998) it makes sense to have members of your clone spreading the load (risk), from short-distance hops (trivial flights), with the chance that the next door plant might be just as bad as the one left behind and within easy reach of natural enemies, but with a higher chance of survival and reproduction, to long distance migratory flights, with the reduced probability of finding a host plant but with the chance that it will be high in nutrition and low in natural enemies.

What clever beasts aphids are 😉

 

References

Dixon, A.F.G. (1998) Aphid Ecology, Second edn. Chapman & Hall, London.

Leather, S.R., Wellings, P.W., & Walters, K.F.A. (1988) Variation in ovariole number within the Aphidoidea. Journal of Natural History, 22, 381-393.

Shaw, M.J.P. (1970) Effects of population density on the alienicolae of Aphis fabae Scop.II The effects of crowding on the expression of migratory urge among alatae in the laboratory. Annals of Applied Biology, 65, 197-203.

Walters, K.F.A. & Dixon, A.F.G. (1983) Migratory urge and reproductive investment in aphids: variation within clones. Oecologia, 58, 70-75.

Ward, S.A., Leather, S.R., Pickup, J., & Harrington, R. (1998) Mortality during dispersal and the cost of host-specificity in parasites: how many aphids find hosts? Journal of Animal Ecology, 67, 763-773.

Wellings, P.W., Leather , S.R., & Dixon, A.F.G. (1980) Seasonal variation in reproductive potential: a programmed feature of aphid life cycles. Journal of Animal Ecology, 49, 975-985.

 

Post script

It is possible that there are some aphids that never fly – Aphids from the genus Stomaphis have incredibly long mouthparts (they all feed through tree bark), and as far as I can tell from perusal of

Stomaphis query aceris

Roger Blackman and Vic Eastop’s monumental work, alate morphs have never been described (or seen) and even males are apterous.

Blackman, R.L. & Eastop, V.F. (1994) Aphids on the World’s Trees. CABI, Wallingford.

 

Post post script

For a very detailed and thoughtful review of the ‘decisions’ and costs involved in aphid reproductive and dispersal biology see Ward, S.A. & Dixon, A.F.G. (1984) Spreading the risk, and the evolution of mixed strategies: seasonal variation in aphid reproductive strategies. Advances in Invertebrate Reproduction, 3, 367-386.

 

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